1. Field of the Invention
The disclosure relates to an electrochemical cell including a spiral wound electrode assembly and to a method of winding the electrode assembly in the spiral configuration. In particular, disclosure relates to an electrochemical cell including a spiral wound electrode assembly having a polygonal shape when viewed in cross-section, and to a method of spiral winding the electrode assembly to have a polygonal shape.
2. Description of the Related Art
Battery packs provide power for various technologies ranging from portable electronics to renewable power systems and environmentally friendly vehicles. For example, hybrid electric vehicles (HEV) use a battery pack and an electric motor in conjunction with a combustion engine to increase fuel efficiency. Battery packs are formed of a plurality of battery modules, where each battery module includes several electrochemical cells. The cells within a module are electrically connected in series or in parallel. Likewise, the battery modules within a battery pack are electrically connected in series or in parallel.
Some battery packs used with conventional hybrid electric vehicles are designed to provide a relatively high voltage, for example 400 volts (V). To achieve the high voltage, battery packs include hundreds of electrochemical cells, and thus may be very large. To reduce the space requirements of the battery pack, improvements in space utilization (volumetric efficiency) within the battery pack, the module and the cell is desired.
Different cell types have emerged in order to deal with the space requirements of a very wide variety of installation situations, and the most common types used in automobiles are cylindrical cells, polygonal (i.e., prismatic) cells, and pouch cells. Regardless of cell type, each cell may include a cell housing and an electrode assembly disposed in the cell housing. The electrode assembly may be provided, for example, in a stacked configuration or a rolled configuration. The stacked configuration may include a series of stacked positive electrode plates that alternate with negative electrode plates and are separated by intermediate separator plates. The rolled configuration may include an electrode pair formed of an elongate positive electrode stacked with an elongate negative electrode and separated by a separator. The rolled configuration may be formed by winding the electrode pair on a mandrel. For example, the mandrel may be rotated about a winding axis, and the electrode pair is wound onto the mandrel. The mandrel is often circular in cross-sectional shape, and the electrode pair wound onto it forms a winding having a cylindrical shape. Although spindles having a rectangular or flat shape have been used to try to form a winding having a rectangular cross-sectional shape, the outer layers of the resulting winding may have rounded corners, where the radius of the rounded corners increases with the number of turns of the winding.
The volumetric efficiency of a polygonal cell that includes a wound electrode assembly is low relative to other configurations since the electrode assembly may include rounded corners that do not fill interior corners of the polygonal cell housing. A need exists for improved usage of the internal volume of a polygonal cell that includes a rolled electrode assembly.